habitable planets of binary stars

Two key questions arise when considering whether life could
evolve in a binary or multiple star system. They are: (a) is it possible
for planetary systems to form around such stars, and (b) if it is, can planets
orbit so as to provide tolerable surface conditions for biological activity?

On the subject of planet formation, it has been suggested that the gravitational
disturbance caused by another nearby star might prevent material from settling
into a stable protoplanetary disk.
However, evidence is now to hand of such a disk around one of the stars
in a young binary system. Assuming then that planets do form, could they
support life? Before 1960, it was generally thought not. Then the Chinese-American
astronomer Su-Shu Huang showed that there
existed various special orbits in which a planet could move in a two-star
system and enjoy clement, stable temperatures.

Basically, there are three possibilities: a wide, roughly circular path
around both stars, a figure-eight orbit around both stars, or a small orbit
around just one star. The exact circuits required for habitability would
depend on details such as the type of stars involved and their separation
distance. Due to its proximity to the Sun, the Alpha
Centauri system has been widely discussed in this regard.

In fiction, Brain Aldiss has speculated what effects the climatic swings
of a planet circling around a binary star might have on the social structures
of its inhabitants. In his Heliconia series, he looks at life and
culture on a world orbiting in a complex planetary system of a binary star
such that its seasons lasts hundreds of years.